Here's the scoop as I understand it on this issue. First let me state that I have or
have had both on my car. Both being the PFS hooked into a standard O2 and heated O2
as well as the fancy $2000 wide range lambda which happens to be built into my Motec
currently on the car. The 4 wire wide range sensor can be had for a little less than
$400 but yes that's what's there.

I'm not up on my reading with respect to the function of the wide range, but have
done a reasonable amount on the normal and heated O2's in the past.

Accuracy

A normal O2 is actually very accurate, but only in a certain range which happens to
be close to stoich or 14.7 : 1 or .45 volts as an output from a normal sensor. What
happens is that the further from stoich you go with a normal O2 sensor the numbers
become more inaccurate with respect to an actual oxygen ratio present. A wide range
sensor is just like its name suggests, more accurate than a normal sensor at mixtures
further from stoich.

Relative Numbers

I'm currently using a wide range for the motec, because that's the only thing it
supports as well as my car being so far from any known 3rd gen configuration I can't
use relative numbers. In this case I'm not speaking of the PFS data logging of
numbers, only what is displayed on the older boxes with keypad. I would differ with
what others have stated in that you should ignore the numbers displayed from a normal
O2 sensor. While you can't extrapolate an actual AF ratio from the voltage on a
normal O2 sensor once it deviates any significant amount from stoich you can use the
voltage as a benchmark that others have used with success. If you recieve the same
voltage as another person has on a normal O2 sensor you can assume that your AF is
similar to theirs at that given time.You may not know exactly what AF that happens to
be but you really don't need to know. Since we do have relative numbers that have
worked for others in the past I would suggest that you can safely tune your car
within reason using numbers from a standard O2 sensor up to the point of about
450+HP. So what voltage numbers are reasonable? From my experience of a few years
doing it that way I found a good benchmark of .82 volts to be the leanest you want to
allow during WOT and higher boost, above 10-12psi. Voltage higher than that will be
richer and a bit safer until you reach a point of being excessively rich, which can
actually cause damage of its own, such as clogging cats, diluting lubrication in the
housings etc. So .82 -.86 is a good balanced range to be in. Just watch the keypad
numbers at wide open throttle in 3rd and 4th gear at 5000-8000 RPM. The number should
remain fairly constant. If the numbers drop below .82 let off the throttle and
increase the fuel in that range and test again. If higher than .86 remove fuel from
that range and test again. A little side observational info. When running leaded race
gas the heated O2 does read a slight bit differently given all other conditions being
the same. Off the top of my head it was about .76 = .82 or something like that. If
someones using C16 or something ask me directly about numbers to be used.

________________

From: Rob Robinette

How the O2 Sensor Works

The oxygen sensor detects oxygen in the exhaust in a way similar to a
battery cell. Platinum layers on the inside and outside of the probe act as
electrodes. Zirconium dioxide between the layers of platinum acts as an
electrolyte. The inside layer of platinum is exposed to the air in the
engine bay, the outer layer is exposed to the exhaust. When the O2 sensor
is hot it generates positive voltage between the two layers of platinum.
Negatively charged oxygen ions in the exhaust are attracted to the platinum
and reduce the voltage that the Engine Control Unit and air/fuel gauge
reads.

That's why a rich mixture = higher voltage from the sensor (more gas
= fewer negative O2 ions to drop the voltage) . Just remember "L=L", Lean =
Low voltage. You can attach a Volt Ohm meter (black to ground, red to the
O2 sensor) to monitor your engine's air/fuel ratio. Full throttle with 0.82
volts is best performance but slightly higher voltage (richer) is safe. At
part throttle the ECU will bounce the ratio from rich to lean. You only
have to worry about full throttle. I suggest you have a copilot read the
voltage while you accelerate at full throttle.

The 3 wire sensors are used to give power and ground to pre-heat the sensor
so it starts working quicker, it has no effect after the sensor gets warmed
up.